UNDERSTAND HOW TO SET UP AND RUN A HYDRAULIC MODEL IN HEC-RAS CREATE A FLOOD INUNDATION MAP IN ARCGIS.

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1 CE 412/512, Spring 2017 HW9: Introduction to HEC-RAS and Floodplain Mapping Due: end of class, print and hand in. HEC-RAS is a Hydrologic Modeling System that is designed to describe the physical properties of streams and rivers, and to route flows through them. Given the discharge computed by HEC-HMS or by other means, HEC-RAS computes the resulting water surface elevation. Using a program HEC-GeoRAS, these elevations can be mapped in ArcGIS to form a flood inundation map. In this exercise, you will run a HEC- RAS model for a particular location on Brushy Creek and use ArcGIS to create the corresponding floodplain map. AFTER COMPLETING THIS EXERCISE, YOU WILL BE ABLE TO UNDERSTAND HOW TO SET UP AND RUN A HYDRAULIC MODEL IN HEC-RAS CREATE A FLOOD INUNDATION MAP IN ARCGIS. Copy data from (drive W:) and place on the C drive under the temp folder(c:\temp\). Do not place in your User folder. Copy data above it. Open HEC-RAS. 2. Open existing HEC-RAS Model To open an existing HEC-RAS model, click on RAS File -> Open Project and navigate to the UB100yr2.prj file. This is a file for a HEC-RAS model for the confluence of Brushy Creek and South Brushy Creek at Walsh Drive.

2 Hit OK to load the project. HEC-RAS contains a series of Elements, and in this project, let s start with the Geometric Data. From Edit menu, select Geometric Data.

3 Open the Cross-Section Editor

4 By using the Up and Down arrows you can navigate along the river cross-sections. By changing the Reach you can switch from Upper to Lower Brushy Creek. By changing the River you can switch from Brushy Creek to South Brushy Creek. Examine the cross-sections in the model. The River Station gives the distance in feet from the most downstream end of the River. In this case feet is the distance from this cross-section on Brushy Creek to the most downstream point on this creek shown in this model. To be turned in: Determine the distance in feet from the upper most to the lower most cross-section on Brushy Creek (Upper Brushy to Lower Brushy Creek, not including South Brushy Creek). How many cross-sections are there in this distance? What is the average distance between the cross-sections? Repeat this calculation for South Brushy Creek. Describe in words the cross-section at Station on Brushy Creek: a). What value of Manning s n is used? b). What is the distance to the next downstream cross-section (ft) for the Left Overbank, Channel and Right Overbank flows? c). What is the lowest elevation of the stream bed (ft above datum)? d). What is the highest elevation of a point in the crosssection? e).what is the horizontal length of the cross-section (ft)? Close the Geometric Data window. Now, let s review the steady flow data. From Edit menu, select Steady Flow Data.

5 These flows are approximated values taken from the HEC-HMS model for the flows during Tropical Storm Hermine on Upper Brushy Creek. The Lower Reach has the total flow of 18,800 cfs, which is divided into 16,300 cfs for the Upper Reach of Brushy Creek and 2500 cfs for the South Brushy Creek (the flow that comes from Dam 7). If you click on the box that says Reach Boundary Conditions you ll see a display like that shown below. What this means is that at the downstream end of the lower reach, the Boundary Condition is set at the Normal Depth for a bed slope of The other two reaches have their downstream boundary condition for depth equal to the upstream depth of the Lower Reach of the main Brushy River. Close the Steady Flow Data window. 3. Run Steady State Model Frim HEC=RAS Run menu select Steady Flow Analysis The Steady Flow Analysis form shows.

6 Click on Compute. The model will run. Close the run and Steady Flow Analysis forms. Click on View profiles button ( stream sections. ) on HEC-RAS interface. Review longitudinal profiles for the three

7 Click on View cross sections button ( surface elevations at cross-sections. ) on HEC-RAS interface. Review cross-sections and water

8 Click on View 3D multiple cross section plot button ( and water surface elevations at cross-sections. ) on HEC-RAS interface. Review cross-sections

9 Click on View summary output tables by profile button ( ) on HEC-RAS interface. Review results.

10 Change the Profile Plot and then open the Summary Output Table for the new profile to get the three tables describing the water surface profile in the three reaches. To be Turned in: Calculate the average velocity over all cross-sections in each of the three reaches (ft/sec). Using these data and the plots of the water surface profiles, describe what is controlling the water surface elevation in South Brushy Creek for the reach we have analyzed. 4. Export results to GIS format From HEC-RAS File menu select Export GIS Data.

11 Populate the form and export the data. And you ll see that this file has been created:

12 Open ArcGIS and in Customize Toolbars, select the HEC-GeoRAS option. Save the ArcMap document as BrushyCreek.mxd Here is what the ArcGIS display looks like with the HEC-GeoRAS extension loaded:

13 You need to have the Spatial Analyst and 3D Analyst extensions of ArcGIS to run this tool. You can check whether you have these extensions by using Customize/Extensions 5. Generate floodplain in GIS Open an existing ArcMap GeoRAS project (use icon shown on next line). Make sure GeoRAS toolbar is active. Save the project. Click on Import RAS SDF File button ( ) from GeoRAS toolbar (this step converts the sdf file into an XML formatted file it does not actually import the data).

14 Select the sdf file created in previous step (this is of RAS Export type). Note the name of the output file (same as the input file but with xml extension). Click on OK to perform the format conversion. Don t worry about an error message saying that this XML file already exists. Define the new import project by running Layer Setup (from RAS Mapping menu on the GeoRAS toolbar). Define:..i. Name of the new analysis (HermineDam)..ii. Name of the RAS GIS export file (UB100yr2.RASexport.XML). iii. Which terrain dataset to use (ubcaoi).. iv. Output directory..v. Rasterization cell (accept default). vi. The completed form should look like the following figure.

15 Click on OK. A new data frame will be created with the name matching the name of the analysis, with the specified terrain dataset loaded in it. The actual import of the data has not been performed yet. (The terrain is turned off by default, so the new data frame will appear empty). Save the project. Import GIS data (RAS Mapping -> Import RAS Data). The process might take few minutes depending on the complexity of the results. During the process, several informative messages will be displayed in the form. Wait until it give message import was successful.

16 GIS representation of the BankPoints, Velocities, Water Surface Extent, River2D centerline, XS Cut Lines (these are the lines that were cut on the Digital Elevation Model to get the original cross-sections, the Bounding Polygon around the dataset. Explore the created dataset.

17 If you turn on only the DEM, ubcaoi, here is what you will see. UBCAOI stands for Upper Brushy Channel Area of Inundation.

18 Create water surface TIN (water surface bound only by the extent of the bounding polygon) by running Water Surface Generation function (from RAS Mapping -> Inundation Mapping menu). TIN stands for Triangulated Irregular Network, which is another way that GIS uses to form surfaces by connecting points and lines into triangles. a. Select the profile for which to create the water surface TIN. In our case there will be just one profile (PF1). b. Check Draw Output Layers if you want to display the TIN (you might not want to do that if you select many profiles to generate at one time).

19 c. Select other options for smoothing and merging floodplain polygons (normally, keep these options unchecked). Here is the resulting TIN. Generate floodplain and water depth (by running RAS Mapping -> Inundation Mapping -> Floodplain Delineation Using Rasters function). a. Select one or several profiles for which to create the floodplain extent (depth grid will be created automatically). Only those profiles processed in step one will be available for processing. b. Check Draw Output Layers if you want to display the output layers. c. Check Smooth Floodplain Delineation if you want to smooth the output floodplain polygon (but you should not do that in the initially). d. For each selected profile, a depth grid and a floodplain polygon feature class will be created. And the following result appears!! What is happening here is that the TIN of the water surface is converted to a grid, and then the grid of the land surface elevation is subtracted from it to form the grid of the water depths shown below.

20 Review the results. Relate the floodplain shape and behavior to the assumptions of 1-D flow in RAS. Pay special attention to the following: a. Where floodplain polygon extends all the way to the bounding polygon. This might indicate locations where cross-sections were not defined wide enough. b. Where there is a break in floodplain polygon. This might indicate that cross-sections were not placed close enough. c. Where there are isolated flooded areas (either on the cross-section or not). This might indicate isolated areas that should not be included as the flow contributing areas. d. Where there are flares in the floodplain. e. Where flow path lines (used to determine distances between cross-sections) are not within the floodplain. f. If water surface extent points are not on the floodplain boundary. g. Other unusual floodplain features. If you use the Identify tool on the layer d PF 1, you can check values of the grid of the water depth.

21 To provide some perspective of the background to this analysis, let s add a Basemap: Choose the option for Imagery And you ll get a rather nice display of the floodplain drawn over a map of Brushy Creek near Walsh Dr.

22 If you turn on the XS Cut Lines and zoom in you can see a rather nice map of the floodplain and the cross-sections used to create it in the neighborhood of the homes we visited when we were on our field trip earlier this semester. Pretty cool!

23 To be turned in: A snippet showing the floodplain of Brushy Creek in the area of Walsh Drive. May need to add map with street names. Summary of items to be turned in: 1. Determine the distance in feet from the upper most to the lower most cross-section on Brushy Creek (Upper Brushy to Lower Brushy Creek, not including South Brushy Creek). How many cross-sections are there in this distance? What is the average distance between the cross-sections? Repeat this calculation for South Brushy Creek. Describe in words the cross-section at Station on Brushy Creek: a). What value of Manning s n is used? b). what is the distance to the next downstream cross-section (ft) for the Left Overbank, Channel and Right Overbank flows? c). what is the lowest elevation of the stream bed (ft. above datum)? d). what is the highest elevation of a point in the cross-section? e).what is the horizontal length of the cross-section (ft.) 2. Calculate the average velocity over all cross-sections in each of the three reaches (ft/sec). Using these data and the plots of the water surface profiles, describe what is controlling the water surface elevation in South Brushy Creek for the reach we have analyzed. 3. A map showing the floodplain of Brushy Creek in the area of Walsh Dr. Print and hand in. Ok, you re done!

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